Cell signaling is widely recognized as a key component in normal cell proliferation and cell death, and in neoplastic transformation. A number of distinct biochemical pathways have been identified within this genre. One of these, the PI-3 kinase (PI-3K or PI3K) pathway (also known as the PI-3 Kinase/AKT pathway), is involved in the production of the second messenger molecule PtdIns(3,4,5)P3 (PIP3). Molecular and genetic studies have shown a strong correlation between the PI-3 kinase pathway and a variety of diseases in humans such as inflammation, autoimmune conditions, and cancers. (See P. Workman et al., Nat. Biotechnol. 2006, 24, 794-796; I. Vivanco et al., Nat. Rev. Cancer 2002, 2, 489-501). The PI-3 kinase pathway controls a number of cellular functions including cell growth, metabolism, differentiation, and apoptosis. Many types of cancer are thought to arise in response to abnormalities in signal transduction pathways such as the PI-3 kinase pathway. The PI-3 kinase pathway comprises a number of enzymes including PI-3 kinase, PTEN (Phosphatase and Tensin homolog deleted on chromosome Ten), and AKT (a serine/threonine kinase also known as PKB) all of which are involved in producing and maintaining intracellular levels of the second messenger molecule PtdIns(3,4,5)P3 (PIP3). Homeostasis of this important second messenger is maintained by PI-3 kinase and PTEN. When either PI-3 kinase or PTEN are mutated and/or reduced in activity, PIP3 levels are perturbed and this perturbation may act as a trigger in the development of cancer. Indeed, both PI-3 kinase and PTEN have been found to be mutated in multiple cancers including glioblastoma, ovarian, breast, endometrial, hepatic, melanoma, gut, lung, renal cell, thyroid and lymphoid cancer. The Class IA isoform of the regulatory subunit of PI-3 kinase, p110α, is frequently over-expressed and mutated in many cancers including gliomas, colon, brain, breast, lung, prostate, gynecological and other tumor types (Ibid.; Y. Samuels et al., Science, 304, 554 (2004)). Thus, a rational approach in treating cancer relates to developing drugs that act on signaling pathways including the kinases of the PI-3 kinase pathway.
The PI-3 kinase family comprises roughly 16 members divided into 3 classes based on sequence homology and the particular product formed by enzyme catalysis. Class I PI-3 kinases have 2 subunits: a 110 kd catalytic subunit and an 85 kd regulatory subunit. Class I PI-3 kinases are involved in important signal transduction events downstream of cytokines, integrins, growth factors and immunoreceptors. Inhibition of class I PI-3 kinase induces apoptosis, blocks tumor-induced angiogenesis in vivo, and increases radiosensitivity in certain tumors.
Other mechanisms for cancer involving loss of a negative regulator have also been identified. For example, PTEN, a lipid phosphatase, regulates signaling through the PI-3 kinase pathway by dephosphorylating PIP3, the product of PI-3 kinase (for review see L. C. Cantley et al., Proc. Natl. Acad. Sci. 1999, 96, 4240-4245). Tumors having mutations in the PTEN tumor suppressor gene have been identified in a number of different cancers. As a consequence of PTEN loss and the resultant increase in PIP3 levels, signal propagation through downstream kinases such as AKT is constitutively elevated. Preclinical studies suggest that this constitutive kinase activation creates a kinase dependency analogous to that in tumors with activating mutations in the kinase itself.
Genetic and biochemical evidence has shown that constitutive activation of AKT can regulate TOR (mTOR in mammalian systems) through phosphorylation of the tuberous sclerosis complex (K. Inoki et al., Nat. Cell Biol. 2002, 4, 648-657). Hence, tumors with loss-of-function mutations in PTEN exhibit constitutive activation of AKT, as well as other downstream kinases such as mTOR, and many tumors in murine models are sensitive to mTOR inhibitors (M. S. Neshat et al., Proc. Natl. Acad. Sci. 2001, 98, 10314-10319).
Therapeutic agents that target key signaling pathways are of considerate interest, LY294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) is a first-generation potent, non-selective inhibitor of PI-3 kinases with an IC50 of 1.4 μM (C. J. Vlahos et al., J. Biol. Chem. 1994, 269, 5241-5248). While LY294002 is an effective inhibitor of PI-3 kinase, and has found utility as a pharmacological tool, it has several undesirable attributes that render it unsuitable for clinical use, including lack of aqueous solubility, poor pharmacokinetics, unacceptable toxicity, lack of tissue specificity, rapid metabolism in animals, and a synthetic route that uses carbon disulfide, a highly toxic compound. As such, LY294002 has never been developed for clinical use but has stimulated the search for improved PI-3K inhibitors of which over 10 are in clinical development and one has received FDA approval.
Tumorigenesis, as well as other disease conditions, may also result from epigenetic-induced changes in gene expression and cellular phenotype in the absence of nucleic acid mutations. Epigenetic effects have been attributed to acetylation of lysine residues on proteins. Three types of proteins appear to be important in this process: the “writers” (i.e., DNA methyltransferase which adds methyl groups to DNA), the “erasers” (i.e., histone deacetylase, HDAC, which removes acetyl groups from histones), and the “readers” (i.e., BET bromodomain proteins, such as BRD2, BRD3, BRD4 and BRDT in humans). A number of bromodomain proteins have been identified and correlated with various diseases. See e.g. Muller et al., Expert Reviews in Molec. Med. 13, 1-21, 2011 herein incorporated by reference. The bromodomain proteins serve as “readers” for chromatin to recruit regulatory enzymes such as the writers and erasers of histone modification which can then lead to regulation of gene expression.
Inhibitors of BET proteins are potentially useful in the treatment of a number of conditions including but not limited to obesity, inflammation, and cancer (A. C. Belkina et al., Nat. Rev. Cancer 2012, 12, 465-477). BET inhibitors act as acetylated lysine mimetics which disrupt the binding interaction of BET proteins with acetylated lysine residues on histones (D. S. Hewings et al., J. Med. Chem. 2012, 55, 9393-9413). This disruption leads to suppression of transcription of genes involved in cancer including c-MYC, MYCN, BCL-2, and some NF-kB-dependent genes (J. E. Delmore et al., Cell 2011, 146, 904-917; A. Puissant, Cancer Discov. 2013, 3, 308-323). For example, B-cell malignancies are associated with the activation of the c-MYC gene which is partially controlled by the PI-3 kinase-AKT-GSK3beta signaling axis (J. E. Delmore et al., Cell 2011, 146, 904-917). MYC (encompassing c-MYC and MYCN) is an oncoprotein that has been difficult to inhibit using small molecule approaches (E. V. Prochownik et al., Genes Cancer 2010, 1, 650-659).
Recently it has been shown that BET inhibition prevents the transcription of MYCN (A. Puissant, Cancer Discov. 2013, 3, 308-323), and blocking PI-3K enhances MYC degradation (L. Chester et al., Cancer Res. 2006, 66, 8139-8146). Therefore, a single molecule that inhibits both PI-3K and bromodomain proteins would provide a novel and potentially more effective way to inhibit MYC activity.
Several recent reviews cover the inception and status of the bromodomain inhibitor field including D. Gallenkamp et al., Chem. Med. Chem., 2014, 9, 438-464 and S. Muller et al., Med. Chem. Commun. 2014, 5, 288-296. Most recently it has been reported that inhibition of BET bromodomain proteins such as BRD4 can prevent the kinome adaptation response (i.e., induced transcriptional upregulation of multiple kinases involved in resistance mechanisms) found for tyrosine kinase inhibitor drugs, such as lapatinib (T. J. Stuhlmiller et al., Cell Reports 2015, 11, 390-404).
The need for more efficacious treatments for cancer and other conditions has lead to combination therapies using multiple anticancer agents, or alternatively multitargeting agents in which a single drug blocks more than one target (See D. Melisi et al., Curr. Opin. Pharm., 2013, 13, 536-542).
It is known that some kinase inhibitors also inhibit bromodomain proteins. For example, LY294002 has been shown to inhibit BET bromodomains (A. Dittmann et al., ACS Chem. Biol., 2014, 9, 495-502) with an IC50 of 12.43 μM on the BRD4 bromodomain protein (binding region 1). Replacing the morpholine group of LY294002 with a piperizine group (LY303511) causes LY294002 to lose all PI3K inhibition activity and, likewise, replacement with a thiomorpholine group causes LY294002 to lose most PI3K inhibition activity (C. Vlahos et al., J. Biol. Chem. 1994, 269, 5241-5248). However, the piperizine replacement compound (LY303511) has been shown to maintain BRD4 inhibition as it exhibits an IC50 of 9.05 μM on the BRD4 bromodomain protein binding region 1 (A. Dittmann et al., ASC Chem. Biol. 2014, 9, 495-502). Other kinase inhibitors have also been found to inhibit BET bromodomains. For example, the PLK1 inhibitor BI2536 and the JAK2 inhibitor TG101209 potently inhibit BET protein BRD4-1 (S W J Ember, ACS Chem Biol., 2014, 9, 1160-1171).
There remains a need for potent inhibitors of PI3K and for potent inhibitors of bromodomain proteins; especially there remains a need for small molecules that inhibit both PI3K and bromodomain proteins such as BRD4. The novel heterocycles of the present invention meet this need by providing compounds with enhanced therapeutic properties useful for inhibiting tumor growth, cancer treatment and other diseases related to aberrant PI3K and/or bromodomain proteins.